1. Field of the Invention
This invention relates to diskless booting and more particularly relates to booting a logical partition from an external disk using a virtual Small Computer System Interface (“SCSI”) connection.
2. Description of the Related Art
A logical partition (“LPAR”) may be created on a computer such as a mainframe computer. Traditionally, an LPAR is created by allocating a processor, memory, and dedicated input/output (“I/O”) devices, and at least one hard disk drive (“HDD”) that is physically within the computer. The computer includes physical resources to support a plurality of LPARS that share the physical computing resources of the computer. The LPAR is booted from the hard disk drive which contains an image of an operating system that runs on the LPAR. An LPAR may be considered a “virtual machine.”
Typically, an application runs on the LPAR. In another embodiment, the application comprises a client application running on another host computer and accesses the computing resources of the LPAR running an application as a server. The LPAR accesses storage devices containing data associated with the application. The storage devices, in one embodiment, are part of one or more storage systems or subsystems of a storage area network (“SAN”). The LPAR accesses the SAN though shared physical I/O devices connected to the SAN and uses SAN drivers to locate and manipulate the data. An application accessing or running on an LPAR is often an application that configures large quantities of data in a database. For example, a financial institution may store financial transaction data on a SAN and may use an LPAR running a financial transaction application.
Typically, applications operating on an LPAR are designed to scale up as demand and use of the applications increases. Scaling up an application of an LPAR requires more and more physical resources of the computer. As the demand for shared physical resources increases, one LPAR may inhibit the performance of other LPARS on the system as the growing LPAR consumes more physical resources. In certain instances, the resource demands of the LPAR grow to the point that they exceed the available physical resources of the computer. Accordingly, it is desirable to migrate the LPAR to a different computer that includes more resources than the first computer in order to support the growth in resource needs of the LPAR.
However, moving an LPAR is complicated because the HDD used to boot the LPAR is local to the first computer. The HDD is physically connected to and located within the first computer. Significant time is required to remove or replicate this local HDD and install the original boot HDD or a copy of the boot image including the operating system on the original HDD on a second computer. If the HDD is damaged or in a physical location different than the second computer, moving the hard disk drive may be impractical or impossible. The process of copying the operating system image is time consuming.
Previous attempts to solve these problems have proposed booting an LPAR from a HDD located external to the computer where the LPAR is located. This booting from an external disk may be called diskless booting and is desirable because a new LPAR on a second computer can be quickly booted from the external HDD that contains the operating system image that was used to boot the first LPAR on the first computer.
Unfortunately, these attempts have had very limited success because specialized and proprietary BIOS must be programmed into the host bus adapters (HBA) of computers that attempt to boot from storage devices on the SAN. The main reason is that booting of an LPAR begins with the BIOS firmware in the HBA and must transition to software that is loaded and configured to identify and access the needed LPAR resources to complete the booting process.
This firmware is proprietary and specific to each hardware vendor requiring low-level application programming interfaces (APIs). This use of proprietary APIs further complicates the matter and tends to require that the computer and the storage devices come from the same hardware manufacturer. There is no common, open, standardized interface for hardware on the computer to communicate with storage devices on the SAN. Some have proposed that the computer enter a Pre-boot eXecution environment (PXE) which would then load a boot agent. However, this would also require standardization between hardware vendors. Others propose a Unified Extensible Firmware Interface (UEFI) standard, which again would require cooperation and agreement between hardware vendors. Because there is no standard BIOS for booting from a HDD on a SAN and no foreseeable agreement on such a standard, other solutions to the problem must be provided.